The Harvard law professor Roger Fisher once proposed placing nuclear codes in a capsule and implanting that capsule in the chest of a presidential aide (“George”) who always carries a butcher knife, so that the only way for the American president to nuke millions of faraway people is to kill one innocent human being with his own hands.

On Tuesday, for the first time in 41 years, a congressional foreign-affairs committee held a hearing to examine who in the U.S. government has the authority to order the use of nuclear weapons. Here’s what the Senate Foreign Relations Committee confirmed: Not only is there no George and no butcher knife, but there’s not much standing in the way of a commander in chief determined to fire nuclear weapons. It was a raw, existential exercise in something that has become routine in Washington since Donald Trump’s election: unearthing and scrutinizing long-buried assumptions about U.S. foreign policy.

“Donald Trump can launch nuclear codes just as easily as he can use his Twitter account,” marveled the Massachusetts Democrat Ed Markey, who earlier this year introduced legislation to prohibit the president from authorizing the first nuclear strike in a conflict without a congressional declaration of war.

“I don’t think we should be trusting the generals to be a check on the president,” Markey said. “I don’t think we should be trusting a set of protocols to be protecting the American people from having a nuclear war launched on their behalf. I don’t think we should be relying on a group of individuals to be resisting an illegal order when they have all been hired by the president.”

“There could be plans in place, right now, in the White House, given to the president, to launch a preemptive war against North Korea using American nuclear weapons, without consulting, [without] informing Congress,” Markey continued, as the hearing wrapped up. “No one human being should ever have that power.”

The experts who testified before the senators didn’t say that Trump could unleash nuclear war with the ease of a tweet, but they did all agree that the president has exclusive authority to use nuclear weapons. That authority doesn’t just derive from the president’s Article II war powers. It also stems from the demands of the Cold War, when the United States needed to respond rapidly in the event of a nuclear attack by the Soviet Union, and from the official consensus, which gradually formed after World War II, that nuclear weapons should be treated differently than other weapons and placed under strict civilian control. (Not all nuclear-weapons states vest sole authority for nuclear weapons in their chief executive; in India and Pakistan, for example, councils are responsible for ordering the use of these weapons.)

The witnesses emphasized that this authority doesn’t mean the president pushes a button or calls up one commander and the military automatically follows the order. Peter Feaver, a political scientist at Duke University, distinguished between “scenarios where the military wake up the president versus scenarios where the president is waking up the military.” When the United States or its vital interests abroad are under attack or judged to be facing imminent attack—when the military wakes up the president—the commander in chief “has a very limited time window to make a decision,” Feaver noted, “and I think we [witnesses] all believe that the system would carry out the order that he gave. The electorate, on Election Day, chose him to make that decision.”

But when the president “wakes up the military,” perhaps “in an extreme funk saying ‘I’m angry and I want something done’ … he requires the cooperation of a lot of people who would be asking” a lot of questions about the context and justification for the strike, which would “slow down” the process, Feaver said. Brian McKeon, the former acting undersecretary for policy at the Defense Department, said that in this scenario, he would expect the president to consult with his National Security Council and other top civilian and military advisers.

Robert Kehler, the former head of U.S. Strategic Command, which oversees the country’s nuclear deterrent, said military leaders could refuse to carry out a presidential order for a nuclear first strike if they and their legal advisers conclude that the military action is unnecessary, excessive, or indiscriminate in targeting civilians—and that the request from the White House is therefore unlawful.

Yet this argument unraveled under questioning. When the Maryland Democrat Ben Cardin asked what these military leaders could do if the president overruled them, Kehler conceded, “Other than to state their view about the legality of the move, the president retains constitutional authority to order some military action. You would be in a very interesting constitutional situation. The military is obligated to follow legal orders, but is not obligated to follow illegal orders.” (McKeon pointed out that while the chain of command for a nuclear first strike might run from the president to the defense secretary to a combatant commander, the president could simply fire and replace the defense secretary or combatant commander if his order is disobeyed.)

“I would [say] ‘I have a question about this’ and I would [say] ‘I’m not ready to proceed,’” Kehler explained.

“And then what happens?” inquired the Wisconsin Republican Ron Johnson.

When the exchange finally ended, unresolved, Kehler, the man whose job it once was to contemplate these very quandaries, let out a sigh of relief.

The committee chairman, Tennessee Republican Bob Corker, had technically called the hearing. But it was the escalating tensions over North Korea’s development of nuclear weapons, and the concerns of Corker and many of his colleagues about Trump’s handling of the crisis, that had forced the issue in Congress after a four-decade hiatus in debating the world’s most destructive weapons.

“We are concerned that the president of the United States is so unstable, is so volatile, has a decision-making process that is so quixotic, that he might order a nuclear-weapons strike that is wildly out of step with U.S. national-security interests,” said the Connecticut Democrat Chris Murphy, who recently sponsored a bill to bar the president from taking military action against North Korea without congressional authorization. “Let’s just recognize the exceptional nature of this moment.”

The North Koreans “don’t have a constellation of satellites to see where we are moving our forces—when [Trump] says an armada is coming, that obviously has to give them some pause,” McKeon noted. “People may say ‘Well, what he says in his Twitter account doesn’t matter. We have policies. We have the leadership of the national command authority—the secretary [of defense] and the chairman [of the Joint Chiefs of Staff], they’ll take care of it.’ That doesn’t compute in Kim Jong Un’s mind—that what the president says doesn’t matter. I would be very worried about a miscalculation based on the continuing use of his Twitter account with regard to North Korea.”

Ultimately, however, the expert witnesses rejected the types of legislative restrictions on the president’s nuclear-weapons authority that lawmakers such as Markey and Murphy have suggested. They claimed that ruling out a nuclear first strike by the United States or requiring, say, Congress or the vice president to sign off on a presidential order to launch nuclear weapons would undermine America’s ability to deter other countries from using their nuclear weapons. The law shouldn’t be changed because of “distrust of this president,” McKeon argued.

James Risch, a Republican senator from Idaho, went further, warning that the North Koreans would closely analyze the hearing and that they needed to understand that the discussion was more “academic” than “practical.”

This talk about “lawyers” and “standards” and “proportionality” is “not a discussion that is going to take place in the heat of battle in today’s world,” Risch said. Any U.S. decision to use nuclear weapons will not be “made by courts or by lawyers or by Congress. It’s going to be made by the commander in chief of the American forces.” And North Korea must recognize that it is dealing with a U.S. president who “will do what is necessary to defend this country … quite quickly if he has to. I want everyone to understand how this works.”

Corker saw his cue to cut in. “I think that’s the reason we’re having the hearing,” he said.

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Uri Friedman is a staff writer at The Atlantic, where he covers global affairs.